Inhibiting Translation Elongation with SVC112 Suppresses Cancer Stem Cells and Inhibits Growth in Head and Neck Squamous Carcinoma

Cancer stem cells (CSC) drive growth, therapy resistance, and recurrence in head and neck squamous cell carcinoma (HNSCC). Regulation of protein translation is crucial for normal stem cells and CSCs; its inhibition could disrupt stemness properties, but translation inhibitors are limited clinically due to toxicity. SVC112 is a synthetic derivative of bouvardin, a plant-derived translation elongation inhibitor. SVC112 had greater antiproliferative effects on HNSCC cells compared with the FDA-approved translation inhibitor omacetaxine mepesuccinate (HHT). SVC112 preferentially inhibited cancer cells compared with patient-matched cancer-associated fibroblasts, whereas HHT was equally toxic to both. SVC112 reduced sphere formation by cell lines and CSCs. SVC112 alone inhibited the growth of patient-derived xenografts (PDX), and SVC112 combined with radiation resulted in tumor regression in HPV-positive and HPV-negative HNSCC PDXs. Notably, CSC depletion after SVC112 correlated with tumor response. SVC112 preferentially impeded ribosomal processing of mRNAs critical for stress response and decreased CSC-related proteins including Myc and Sox2. SVC112 increased cell-cycle progression delay and slowed DNA repair following radiation, enhancing colony and sphere formation radiation effects. In summary, these data demonstrate that SVC112 suppresses CSC-related proteins, enhances the effects of radiation, and blocks growth of HNSCC PDXs by inhibiting CSCs. Significance: Inhibiting protein elongation with SVC112 reduces tumor growth in head and neck squamous cell carcinoma and increases the effects of radiation by targeting the cancer stem cell pool.